Question

Why are Noble Gas symbols often included in the electronic configuration of certain elements?

Answer 1

Well, it gives the configuration of the last Noble Gas.......

Explanation:

For the full electronic configuration of calcium, `Z=20`, I could write out........

`1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)4s^(2)`.....

But of course this a portmanteau of the LAST Noble gas, `"argon,"` `Z=18`, whose electronic configuration is the closed-shell....

`1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)`.....PLUS 2 extra valence electrons that fill the `4s` shell. The use of `[Ar]` to represent this closed-shell, inner core of electrons is perfectly acceptable, and widespread.....

And so...

`underbrace(1s^(2)2s^(2)2p^(6)3s^(2)3p^(6))_"electronic configuration of argon"4s^(2)`.....`-=` `[Ar]4s^2`

How would I represent the electronic configuration of `Na?`